Actually not true. While Torrent Greninja isn't absolute garbage per se, it is not any better than something like Infernape(admittely a lot faster, but without any power on its physical moves). Probably on the viability thread it wouldn't be anything above B lol.T
I don't mean to add fuel to the fire, but I promise you, even if we ban Protean all together, that won't be enough to keep it in OU.
Banning Protean, considering the policy of Smogon, will never be a thing unless the ability becomes very widespread with most if not all its fully evolved users being broken because of it(think about Swift Swim+Drizzle in BW, it wouldn't have been banned altogheter if the problem was Kingdra only).
So that this post isn't completely useless, I feel to add that most faster Pokémon without boosts are Mega Evolutions. This isn't a good thing not only because of the increasing opportunity cost towards slower Mega Evolutions, but in particular because how the first turn mechanics works. It means that if your Manectric, Sceptile or whatever it is has not megaevolved yet you will not be able to revenge Greninja, as such you will have to resort on more "checks", put Protect/Fake Out on your mon or always lead with your Mega Evolutions, all of which are negative things for their own reasons.
Similarly, the defensive aspect of Protean can screw with you if you are resorting on priority. Say, Greninja has just used Gunk Shot, now you are no longer able to revenge kill it with Breloom until it stops being a Poison type; same for all the other priorities except normal/Aerialted Quick Attack and Gale Wings Brave Bird, as no viable Greninja move can allow it to resist these moves.